Debt (Components Of Short-Term Debt) (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Short-term Debt [Line Items]
Short-term debt	$ 965	$ 732
Atlantic City Electric Co [Member]
Short-term Debt [Line Items]
Short-term debt	133	23
Delmarva Power & Light Co/De [Member]
Short-term Debt [Line Items]
Short-term debt	137	152
Potomac Electric Power Co [Member]
Short-term Debt [Line Items]
Short-term debt	231	74
Commercial Paper [Member]
Short-term Debt [Line Items]
Short-term debt	637	586
Commercial Paper [Member] | Atlantic City Electric Co [Member]
Short-term Debt [Line Items]
Short-term debt	110
Commercial Paper [Member] | Delmarva Power & Light Co/De [Member]
Short-term Debt [Line Items]
Short-term debt	32	47
Commercial Paper [Member] | Potomac Electric Power Co [Member]
Short-term Debt [Line Items]
Short-term debt	231	74
Variable Rate Demand Bonds [Member]
Short-term Debt [Line Items]
Short-term debt	128	146
Variable Rate Demand Bonds [Member] | Atlantic City Electric Co [Member]
Short-term Debt [Line Items]
Short-term debt	23	23
Variable Rate Demand Bonds [Member] | Delmarva Power & Light Co/De [Member]
Short-term Debt [Line Items]
Short-term debt	105	105
Term Loan Agreement [Member]
Short-term Debt [Line Items]
Short-term debt	$ 200